1. Technical Field
The present invention relates to manufacturing methods of a nozzle plate having nozzle holes to discharge droplets. The invention also relates to nozzle plates, droplet discharge head manufacturing methods, and droplet discharge heads.
2. Related Art
An inkjet head installed in, for example, an inkjet recording apparatus is a known example of a droplet discharge head that uses a nozzle plate for the discharge of droplets. Such inkjet heads generally include a nozzle plate having a plurality of nozzle holes provided for the discharge of ink droplets, and a cavity plate bonded to the nozzle plate and that includes ink channels such as pressure chambers and a reservoir in communication with the nozzle holes of the nozzle plate. The pressure applied to the pressure chambers by a driving section causes the ink droplets to discharge through selected nozzle holes. The driving method includes a scheme that uses electrostatic force, a piezoelectric scheme that uses a piezoelectric element, and a Bubble Jet® scheme that uses a heater element.
In response to the recent demand for high-quality inkjet head in terms of print and image qualities for example, there is a strong need to improve density and discharge performance. Under these circumstances, various ideas and proposals have been set forth concerning the nozzle portion of the inkjet head.
To improve ink discharge characteristics, it is desirable to adjust the channel resistance in the nozzle hole portion, and to adjust the substrate thickness to provide the optimum nozzle length. Another way to improve discharge characteristics is to align the direction of ink pressure on the nozzle with the nozzle axial direction through the use of a two-stage nozzle having a first nozzle portion (ink discharge side) and a second nozzle portion (ink supply side) of different inner diameters, instead of a nozzle that is cylindrical throughout.
A nozzle plate having the nozzle holes of such a multistage structure can be manufactured by the following method. Specifically, a two-stage depression that eventually becomes a first nozzle portion and a second nozzle portion is formed by the anisotropic dry etching of one of the surfaces of a silicon substrate using ICP discharge. Then, a liquid-resistant protective film (SiO2 film) having ink resistance is formed by thermal oxidation over the silicon substrate. With this surface of the silicon substrate supported on a support substrate, the thickness of the silicon substrate is reduced by grinding from the other surface (hereinafter, “discharge face”). The bottom of the two-stage depression is removed in the process of thickness reduction, and as a result a two-stage nozzle is formed. With the etched surface of the silicon substrate supported on the support substrate, a liquid-resistant protective film having ink resistance is formed on the discharge face, which is then subjected to an ink repellent treatment. Here, the inner wall of the nozzle hole (the first nozzle portion and the second nozzle portion) is also subjected to an ink repellent treatment. Then, a support tape is attached to the discharge face, and the support substrate is detached. The ink repellent layer remaining on the inner wall of the nozzle hole is then removed by performing a plasma treatment from the etched surface. The support tape is then detached to complete the nozzle plate (see, for example, JP-A-2007-168344; FIG. 5 to FIG. 8).
In the foregoing publication, grinding is performed from the bottom side of the depression (discharge face side) after forming the two-stage depression that eventually becomes the nozzle hole. This causes a defect called chipping on the periphery of the discharge opening of the nozzle hole, leading to a reduced yield.
Further, because another liquid-resistant protective film is formed on the discharge face after forming the liquid-resistant protective film on the inner wall of the nozzle hole, there is a boundary between these liquid-resistant protective films. Such boundaries cause the ink droplets to seep in and cause damage to the silicon substrate under protection. The boundaries are particularly problematic because they occur at the discharge opening portion of the first nozzle portion where high dimensional accuracy is required. Accordingly, there is a strong need to overcome such problems.
As described, the first nozzle portion having the discharge opening requires very high accuracy. In this regard, the technique disclosed in the foregoing publication fails to provide sufficient diameter accuracy for the discharge opening, because the first nozzle portion is formed by two rounds of etching that proceeds deep down towards the surface where the discharge opening is formed.